,^5 






A Study of the Changes in Skins During 
Their Conversion into Leather 

A thesis Submitted in partial fulfillment of the requirements for the 
Degree of Doctor of Philosophy in the University of Michigan 



By 



Anton Augustus Schlichte 



Reprinted from 

The Journal of the Americon Leather Chemists Association 

December-November, 1915 



Copyright, 1915 



«<''' 

^*v 



Meinen lieben Eltern in 
Dankbarkeit gewidmet 



CONTENTS. 



acknowxkdgkment 3 

Introduction 3 

Study of Microscopic Changes in Hides during their Conversion 

INTO Leath er 6 

Review of Literature 6 

Experimental Work on Technique of Imbedding and Cutting Tissue 7 

(a) Paraffine Methods 7 

(b) Celloidin Methods 9 

(r) Freezing Method 10 

Study of Changes in Structure during Tanning 12 

Study oe Changes in Volume and Weight of Cai^fskins during the 

Liming Process 14 

Apparatus 15 

Experimental Work on Calfskins 17 

Attempts to Remedy Thinness of Flank 34 

Results 39 

Study of Deputation in Sterii^e Limes 42 

Review of Literature 42 

Experimental Work 43 

(a) The Sterilization of Skins 46 

(h) Laboratory Tests on Depilation 48 

(r) Depilation and Subsequent Tannage 56 

Conclusion 60 

BiBIJOGRAPH y 62 



Gift 
ba Univertity 



J 



ACKNOWLEDGKMKNT. 

The generosity of Mr. Carl E. Schmidt in establishing a fel- 
lowship in tanning at the University of Michigan, has enabled 
the author to pursue for 3 years, the studies outlined in this 
thesis. Mr. Schmidt has, moreover, given freely of his time and 
experience and it is a pleasure at this time to express apprecia- 
tion, not only for the financial assistance rendered but more es- 
pecially for the able counsel so unstintedly afforded. 

Acknowledgement is also due Mr. V. A. Wallin for his interest 
and courtesy in making possible the completion of the experi- 
ments on heavy leathers. 

The author wishes to thank sincerely, Prof. A. H. White for 
his constant interest and hearty co-operation during the entire 
time consumed by this research. 

Introduction. 

The use of hides both as skins and leather for protection 
against cold and rain, for weapons, or for ornaments, dates back 
to the remotest history of man. 

While the hides were tanned in the earlier times with the hair 
on, methods were soon found to remove it and thus improve the 
product. The first substance used was probably wood ashes and 
this continued as the standard for some time. After tanneries 
were established, for up to this time the tanning was done only 
on a small scale, new substances were sought for, and lime, one 
of the oldest depilatory agents, was used. The method followed 
was to slack the lime in pits and soak the hides in a saturated 
solution of calcium hydroxide. This method although slightly 
modified has remained practically the same for centuries. 

The tanning process was and is in general the following: 

I. Hides are soaked to remove blood and dirt and to bring 
them back as nearly as possible to their original condition. 



4 A STUDY OF the: CHANGES IN SKINS 

2. They are placed in pits containing- milk of lime, bacteria 
being always present and sulphides being frequently added, for 
from 3 to 1 8 days until the hair "slips" easily, that is, can be easily 
removed. 

3. They are then bated to remove lime and bring the skin into 
the desired physical condition. The bate may be either acid or 
bacterial. 

4. The next step is the pickling process in which the skins are 
treated usually with salt and sulphuric acid. 

5. Then follows the tanning process proper, which may be 
either a mineral or a vegetable tannage. 

6. The last step is a tinishing process. 

The entire tanning process has thus far been outlined to show 
the dependence of the finished product upon the correct perform- 
ance of each succeeding step of the process. It is only through 
tests on the finished leather that the effect of any alteration in 
any step of the process can be detected. 

The liming process is the one studied in greatest detail in this 
paper but any changes due to this operation can be detected only 
in the finished product. Moreover, the method of soaking must, 
because of its influence, also be specified. The object of soaking 
hides is to cause them to resume as nearly as possible their orig- 
inal clean and pliable condition. This part of the process while 
not so important when green hides are used becomes a matter of 
great importance when dried hides are to be investigated. The 
length of soaking, number of changes of water and the acids or 
alkalies which may have been added, all have an effect on the final 
product. Should the hides be soaked too long or should the water 
not be renewed frequently enough, bacteria multiply and a part 
or, in extreme cases, all of the hide may be lost. On the other 
hand acids and alkalies cause swelling of the hide and if too much 
of either be added the hide will be "plumped" too much.^ This, 
while not fatal to a good final product, has its disadvantages and 
as a rule causes trouble. 

The object of liming is not alone the removal of the hair but 
also the loosening of the fiber bundles. More surface is thus ex- 
posed and hence the tanning agents are taken up more readily. 
' Jettmar Handbuch, p. 56. 



A STUDY OF the: CHANGES IN SKINS 5 

In the vegetable tannage this makes a heavier leather. In the 
mineral tannage the loosening of the fiber bundles makes a more 
pliable leather.- The latter object is of great importance in the 
chrome tannage which is the method most used in manufacturing 
light or upper leathers. The hides after soaking are placed in 
pits in which an excess of calcium hydroxide is always present 
and to which some sodium or arsenic sulphide may or may not 
have been added. The hides are ''hauled," that is, taken out and 
the. lime ''bettered" once a day until the hair "slips" easily. It 
requires much practice and experience before one is able to tell 
exactly whether a hide is done or not, and the method is not only 
unsatisfactory but also very unscientific, for the personal equa- 
tion of the operator plays too important a part. The hides are 
then soaked in warm water, paddled and beamed. In the latter • 
process the skin is placed over a piece of wood semi-circular in 
cross section and the hair is removed with a blunt knife. The 
long hairs comes off very easily but the fine or "ground" hair and 
the pigment, especially in the case of black skins, cause some 
trouble. Part of the intercellular substance, corium, "scud" or 
"gneiss" and some lime soaps^ are also removed in this treatment 
The next operation, "bating," has as its main object complete 
removal of the lime remaining from the previous treatment. The 
loosening of the fiber bundles, however, is also materially aided 
by bating and this, as before mentioned, is, in the case of light 
leather, of greatest importance. The bates most commonly used 
owe their activity to bacteria and are frequently more or less un- 
satisfactory and harmful to the skins. Bates of known bacterial 
cultures are used somewhat and give good results, but the most 
common ones consist of organic acids such as butyric, lactic, etc. 
The skins are then pickled. The pickling consists usually of a 
treatment with sulphuric acid and salt. One object is to partially 
reduce the excessive swelling caused by the bate. Another, 
without doubt, is to furnish some free sulphuric acid which is 
considered necessary in the subsequent chrome bath. This sul- 
phuric acid is probably absorbed by the skin and thus carried 
over to the tan bath. This finishes the treatment received by the 
^ Gerber, No. 938, p. 253; Procter's Principles of Leather Manufactur- 
ing, p. 126. 

^ Procter's Principles of Leather Manufacture, p. 136. 



6 A STUDY OF the: CHANGES IN SKINS 

skins in the "Beam House," which is probably the most im-' 
portant division of the tanning process. The most important part 
of the beam house work is the hming process, and hence this was 
made the object of the subsequent investigations. The object was 
to gain some insight if possible, into this apparently simple but 
actually very complicated process and to furnish something of 
practical value to the industry. 

It seemed obvious that some accurate way of controlling the 
liming and of judging the product afterward was absolutely 
necessary in order that improvements could be noted. The ordin- 
ary method of judging the product by the "feel" left much to be 
desired and it was recognized that the personal equation had to 
be eliminated as much as possible if anything of real value were 
to result. The most natural idea was to obtain some means of 
following the action of the lime step by step. This could not be 
accomplished with the naked eye and hence the assistance of the 
microscope was necessary. A review of the literature at hand 
showed that although considerable work with the microscope had 
been done the results were not very satisfactory. 

Study of Microscopic Changes in Hides During Their 
Conversion Into Leather. 

Some of the earliest work on the cutting of sections of leather 
was done by Kathreiner in 1879.* This work was never pub- 
lished and on inquiring of Prof. Procter it was found that al- 
though notes had been preserved, they were in no shape to allow 
of their being published. Thus we have no authentic record of 
his work. The next reference found was to some work by Prof. 
Thomas Palmer.^ He applied his method to determine the pene- 
tration of vegetable tanning agents. The sections were mostly 
cut by hand. Some sections after dehydration in alcohol and 
clearing in clove oil were infiltrated with "Strickers" solution 
(gum arabic and glycerine 3:1) and cut with a microtome. In 
some cases he also dehydrated in alcohol two or three hours, 
cleared in a mixture of cedar oil and benzol, infiltrated in a mix- 
ture one part 50° melting point and two parts 40° melting point 
paraffine until transparent, and then changed to a bath of two 
* Procter's »Leather Industries Laboratory Book, p. 424. 
^ Collegium, 1902, p. 325. 



A STUDY OF THE CHANGES IN SKINS 7 

parts 50° melting point and one part 40° melting point paraffine 
for three or four hours. The mixture of cedar oil and benzol 
was in the ratio of three to five. He does not tell of any changes 
noted in the leather, except that the distance to which the tanning 
agent had penetrated could be noted by differential stains. More- 
over he does not give the thickness of the sections cut. Procter, 
in his Leather Industries Laboratory Book, also speaks of cut- 
ting sections by hand and of cutting sections by means of a micro- 
tome, but gives no specific directions. 

M. Henri Boulanger in an elaborate monograph, "Essais du 
Cuir dans ses Applications industrielles. Memoires publies par 
la Societe d'Encouragement pour I'industrie national 1907," part 
of which is published as ''Etude Micrographie du Cuir" in Bulle- 
tin de la Societe d'Bncouragem,ent in 1908, gives some difections 
for cutting sections. The pieces to be cut are placed 12 hours 
in a mixture composed of distilled water 5 grams, pharmaceu- 
tical glycerine 5 grams, acetone 90 grams. They are then dried 
and imbedded in hard paraffine and cut. Another method given 
is to dehydrate in 'gradually increasing alcohol until absolute is 
used, to place in xylol, then in melted paraffine 38° to 40°. After 
several days the tissues are cooled, dried 36 or 48 hours, im- 
bedded in hard paraffine and cut. Although many sections were 
prepared their thickness is not mentioned. One interesting con- 
clusion of the author is that the elastic fibers are well preserved 
and that to them the leather owes its strength and pliability, while 
the connective tissue has been totally changed. This is a remark- 
able conclusion when one takes into consideration that less than 
3 per cent, of the skin is elastic tissue and more than 95 per cent, 
is connective tissue.*' Moreover the elastic fibers have little elas- 
ticity and are the first to rupture when the skin is stretched. 
Their chief function appears to be that of support.^ 

Andreis, in an article on "The Process of Liming"® speaks of 
"taking a transverse section of the hide and noting no horizontal 
layers or channels." He does not give any methods for cutting 
the sections and presumably means that they are to be cut by 
hand. 

^ Reimer, Din^ . Poly. Join ., No. 205, p. 149 (1872). 

^ Hyde, Diseases of the Skin, p. 22 (1909). 

^ JouRNAi,, Am. Leather Chem. Assoc, Vol. VII, p. 609 (1912). 



8 A STUDY O? THE CHANGES IN SKINS 

As none of the references quoted gave definite, concise and 
adequate directions for preparing sections, experiments were re- 
sorted to, in order to find a way to prepare good sections by some 
simple and quick method Having no landmarks to guide us, 
much time was spent in going astray. At this time certain sec- 
tions of rocks were being made by grinding and this method ap- 
peared feasible for leather. The piece of leather to be ground 
was placed in Canada balsam in a tube in hot water and suction 
applied. After two to four hours the leather seemed impregnated 
with balsam and was removed, mounted on a piece of plate glas;3 
I inch square and ground with a carborundum wheel until a 
flat surface was obtained. The piece was then turned over and 
mounted and the grinding continued, until the section was fairly 
thin. Then a finer wheel was used, until the section became very 
thin. It was removed, turned over and mounted on a glass slide 
and the grinding resumed, until the section was as thin as could 
be obtained. These sections showed some fiber bundles but were 
unsatisfactory in three ways. The process was too slow, the 
sections too thick, and a complete section could not be obtained as 
some parts were always torn away in grinding. 

Methods of Imbedding and Cutting Tissues. 

Leather is harder and tougher than ordinary tissue. It is dense 
and requires an unusually long period of infiltration. It is tough 
and offers great resistance to the knife so that the infiltration must 
be very thorough before good sections can be obtained. 

Methods of cutting sections after imbedding in paraf¥ine and 
celloidin and after freezing were studied. Various modifications 
were tried and those giving best results are described in detail, 
although they, are merely modifications of methods used in 
pathology. 

The method of imbedding in paraf¥ine involves the following 
steps. 

I — 95 per cent, alcohol 24 hours, change after 12 hours. 

2 — Absolute alcohol 24 hours, change after 12 hours. 

3— Xylol, I hour. 

4 — Xylol, 2 hours. 

5 — Para|fine 42° melted in an oven from 12 to 24 hours depending 

on size of piece used. 
6 — Parafifine 52° from 24 to 48 hours depending on size of the piece. 



A STUDY OF THE CHANGES IN SKINS 9 

The piece is then taken from the molten paraffine and imbedded 
according to the following procedure. A small dish is greased 
with tincture of green soap or glycerine and placed in cold water. 
Clean ^2° paraffine is melted with a free flame and the molten 
paraffine is allowed to drop into the dish until it has attained a 
depth greater than the thickness of the piece to be imbedded. As 
soon as a film of hardened paraffine has formed on the bottom the 
tissue is removed from its previous bath and placed face down in 
the dish. The surface of the melted paraffine is now cooled by 
blowing on it, and as soon as a fairly thick film has formed the 
whole dish is plunged into ice water. 

In spite of all precautions taken this method was not satisfac- 
tory. All attempts to cut sections of a satisfactory thickness were 
unsuccessful as the tissue was either pulled away from the im- 
bedding material or was torn by the knife. In fact, no com- 
plete thin section could be obtained by this method. Other 
methods based on paraffine infiltration using acetone, clove oil, oil 
of bergamot and aniline were tried and the results were unsatis- 
factory. Even infiltration with paraffine in solution, that is, in 
benzol or xylol, gave poor results. This seems to show that 
ordinary methods cannot be used and that methods like tlie one 
used by Boulanger^ ''infiltrating in melted paraffine 15 minutes 
and then blocking in hard paraffine" cannot give good results. 

The next method tried was the celloidin method. In this the 
dehydration was carried over a longer period so that the presence 
of any moisture was precluded. The procedure was as follows : 

I — 80 per cent, alcohol 12 hours. 

2 — 95 per cent, alcohol 48 hours, changed every 24 hours. 
3 — Absolute alcohol 48 hours, changed every 24 hours. 
4 — Absolute alcohol and ether (equal parts) 24 hours. 
5 — I per cent, celloidin 96 hours. 
6 — 2 per cent, celloidin 120 hours. 
7 — 5 per cent, celloidin 168 hours. 

8 — ID per cent, celloidin 6 days to 2 weeks depending on the size of 
sample used. 

In order that a number of pieces might be imbedded simultan- 
eously they were held in clips tied to strings, which led through 
holes, in the wooden cover of a shallow dish. This dish was filled 
' Bulletin de la Societe d'encouragement, p. 250 (1907). 



lO A STUDY OF THE CHANGES IN SKINS 

with a 10 per cent, solution of celloidin, the cover put on and the 
ether and alcohol allowed to evaporate. The tissues were then 
cut out, trimmed and mounted on wooden blocks. They were 
cut in a microtome under a constant flow of 80 per cent, alcohol. 
The sections obtained by this method, after long practice, were as 
thin as 5 or 7 microns and averaged about 10 to 18 microns. 
These could be examined even with an oil immersion lens. This 
method while giving excellent results had as a very serious dis- 
advantage the long time necessary for good results. Many at- 
tempts were made to shorten this method but none gave good 
results. A very long time is absolutely necessary for perfect 
infiltration. 

Believing that the added knowledge gained by experience might 
after all, enable us to use the paraffine methods, these were again 
tried. The results while better than those first obtained, still left 
much to be desired. The leather tore away from the paraffine 
very easily and it was impossible to cut good sections. The 
paraffine methods had so many advantages both as to quickness 
and simplicity, that many modifications of the method previously 
given, were repeatedly tried. The conclusion finally reached 
was, that none of the paraffine methods would give good results. 
Methods using beeswax, gum arabic, etc., were tried and also 
failed to give good results. 

The only short method which appeared promising was the 
freezing method and this was then tried. This method had the 
obvious advantage of great saving in the time required to 
obtain complete sections. The method was very simple and, 
although much practice and experience were necessary before 
good sections were obtained, the results justified the time spent 
in acquiring the technique. The sample to be sectioned was cut 
from calfskins, i by 2 centimeters and if wet, mounted directly. 
If dry, it was first soaked in water until thoroughly moistened 
and then mounted upon the base plate of a Bardeen microtome 
and covered with a thick solution of gum arabic. The liquid 
carbon dioxide was then turned on and the pieces were frozen 
very gradually. When the right degree of hardness has once been 
obtained the piece should never be allowed to warm up and should 
never be frozen again. This is of great importance as several 



A STUDY OF the: CHANGES IN SKINS II 

freezings will cause important changes in the structure/^ The 
greatest changes are caused by over freezing and if this is done 
excessively, the piece used may crumble and become worthless. 
A slight fixation of the tissue in lo per cent, formol" prevents 
most of the changes due to freezing. The sections when cut 
are placed in a dish filled with water. They are then transferred 
by means of a brush or section lifter to a lo per cent, dextrin 
solution which is kept warm, and floated onto a glass plate, dried 
a few minutes, soaked in absolute alcohol until clear and coated 
by pouring over them a i or 2 per cent, solution of celloidin. 
The plates are placed in warm water and left until the thin 
celloidin sheet floats off. They can now be handled easily and 
quite roughly without any danger of damage. They can be 
stained with alcoholic or aqueous solutions of various dyes. A 
water solution of eosin and also a double stain, first in Weigert's 
haematoxylin and then in Van Giesens^^ mixture were used. The 
latter gave excellent results and enabled one to distinguish the 
various kinds of fibers present, with great certainty. 

The sections were not so thin as those obtained by the celloidin 
method, averaging only 35 to 40 microns, but this was thin enough 
to allow the use of any high power objectives except the oil 
immersion. The sections were very delicate and required great 
care in the preliminary handling. The method requires little 
time. A skilled operator can fix, freeze, stain and mount a com- 
plete section in 30 or 40 minutes. In some cases the time required 
is greater depending on the ease with which the piece in question 
can be cut. Sections from heavy hides during the liming require 
much longer, as the tissue is very delicate and flabby and tears 
very easily. After the hide has been in a tan liquor it can be 
cut very rapidly. This method has not only the advantage of 
speed but also is better in that the tissue is practically the same 
as it was before cutting. The method does not subject the tissue 
to such severe treatment as for instance the dehydration with- 
absolute alcohol, which is necessary in the case of the celloidin 
and paraffine methods. It is true that freezing may dehydrate 
in a certain sense, but the following immersion in water probably 

^•^ Warthin Practical Pathology, p. 215, 

!• Warthin Practical Pathology, p. 216, 

'■- Warthin Practical Pathology, p. 260. 



12 A STUDY OF the: CHANGES IN SKINS 

allows the tissue to resume its previous condition. This seems 
logical, since the freezing lasts a very short time, from 5 to 10 
minutes at the most. 

Study of Changes in Structure During Tanning. 

Before proceeding to the experimental study of tissues prepared 
in the laboratory a considerable number of commercial products 
w^ere examined. Sections were made of various commercial 
leathers such as dongola, waterproof, wax upper, plow grain, 
flesh splits, badger sides, oil grain, reliance calf, dull romar 
sides, kangaroo calf and others. These gave some idea of how 
a finished leather looked. Through the courtesy of Mr. Carl E. 
Schmidt of Detroit, pieces were cut daily from a particular 
calfskin as it went through his tanning process and sent for 
examination. As soon as these samples were received a section 
was made by the freezing method and a piece started by the slow 
celloidin method. This set was kept as a standard of a good 
product and will be referred to as S-22. This set did not, however, 
entirely fulfill its purpose, because the necessity of knowing the 
exact location and orientation of the pieces cut from the hide 
was not discovered until later. This was shown by an examination 
of pieces cut in a systematic manner from a finished calfskin 
(Experiment S-18). Samples were taken from this leather at 
the butt, right and left flank, and neck and carefully infiltrated 
with celloidin. Sections were cut both parallel and at right 
angles to the grain. The sections showed a great difference in 
structure between pieces cut from the flank and from the butt. 
These show the flank to have a much smaller amount of connective 
fibers than the butt and neck. Moreover, the fiber bundles of the 
flank are further apart and in general form a looser network. 
The connective tissue is more wrinkled that is, the folds in the 
individual fiber bundles are more numerous. This apparently 
accounts, at least partially, for the looseness of the flank* after 
tanning. 

This difference between various portions of the same skin was 
further studied in series S-26, by tanning two pieces of calfskin 
cut so that one piece was almost entirely flank while the other 
was along tl\e backbone. Small pieces were cut daily from adja- 
cent portions of each skin, one from the backbone and the other 



A STUDY OF the: CHANGKS IN SKINS 



13 



from the edge of the flank, and sections were prepared by the 
freezing method using the Van Giesen stain. Sections were cut 
both parallel and at right angles to the backbone in each instance. 
These showed the same looseness in structure in the fresh flank 
as was evident in the finished leather. 

This subject was pursued still more systematically in Series 
S-36 where a whole calfskin was trimmed to an approximate 
rectangle and divided into six pieces. This work is referred to 
again in the discussion of volume changes where the details are 
given. 

Through the courtesy of V. A. Wallin of Grand Rapids, samples 
of a certain cow hide were sent throughout the tanning process. 
The pieces were taken so that the sections made therefrom could 
be cut parallel and at right angles to the backbone. Samples 
were received during the following stages of the tanning process. 
All sections were cut by the freezing method. 

— Washed hide — originally a green salted one. 

— After 24 hours in lime. 

— After ^2 hours in lime. 

— After 96 hours in lime. 

— Out of hot water. 

— Into cold water. 

— Out of cold water. 

— Out of rockers — in 8 days. 

— Out of hang yard — in 4 days. 

— Out of first layer — in 5 days. 

— Out of second layer — in 9 days. 

— Out of third layer — in 15 days. 

— Out of fourth layer — in 22 days. 

— Out of fifth layer — in 28 days. 

— Out of wet dip — in 15 days. 

Out of tempering vats — in 2 days. 
— Out of bleach. 

Out of oil wheel. 

Finished leather. 

In these various experiments about 125 different blocks were 
prepared, from which 600 specimens were cut, stained and 
mounted. A careful examination of all these sections gave, how- 
ever, rather meager results. The changes from day to day are 
so gradual and the diflferences in structure of diflferent portions 
of the same hide are so pronounced that it is extremely difficult 



No. 


I. 


No. 


2.- 


No. 


3-- 


No. 


4.- 


No. 


5-- 


No. 


6.- 


No. 


7.- 


No. 


8.- 


No. 


9- 


No. 


10.- 


No. 


II.- 


No. 


12.- 


No. 


13.- 


No. 


14.- 


No. 


15-- 


No. 


16.- 


No. 


17.- 


No. 


18.- 


No. 


19.- 



14 A STUDY OF THK CHANGES IN SKINS 

to State the cause for any dififerences observed. The fiber bundles 
become partially separated into fibrils in the liming process, but 
it could not be determined whether these fibrils are hollow or 
solid. In the bark-tanned process the interstices become filled 
with solid material so that the leather becomes firm and of more 
uniform structure. In chrome-tanned leather, the interstitial 
spaces are even greater than in the soaked hide and the fiber 
bundles and fibrils are sharply defined. The flank is undoubtedly 
composed of larger fiber bundles than the butt or shoulder and 
in the former there are larger spaces between these bundles than 
in the latter. 

The idea first held that the microscopic method could be used 
in the tannery, as an accurate check on the process, had to be 
abandoned. The great difficulty was that in a given skin, pieces 
from different parts showed such differences in structure that 
even after long experience one could not tell whether the differ- 
ences shown were inherent in the skin or due to the influence of 
the treatment. 

Changes in Volume of Hides During Liming Process. 

Changes in the volume of hides in the limes are so great as to 
be readily noticed. There have, however, been no quantitative 
data published on this point. The apparatus used for these 
measurements is shown in Fig. i. 

It consists of a brass cylinder A, 2.5 inches in diameter and 

15 inches high. At the bottom a small brass tube B, 0.25 inch in 
diameter leads to an upright 100 cc. glass stoppered burette, C. 
The cover D screws on to the cylinder by means of a very fine 
thread, which insures a water-tight joint. The cover is divided 
into 30 equal divisions on the edge K and a vertical mark is made 
on the cylinder, permitting the cover to be screwed down to a 
definite point or reading. In the center of the cover a hole is 
bored into which a pipe with outside threads £ is soldered. 
Another pipe with inside threads F fits over B. A glass tube G 
with a fine string around it is inserted into B through F and 
screws tight by means of F. This joint is also water tight, if the 
thread has been previously greased. The threads of cover D 
are also greased, anhydrous lanoline proving a good material for 
this purpose. • The glass tube G has a mark, to which the liquid 



A STUDY OF THE) CHANGES IN SKINS 



15 



used is allowed to ascend before a reading is taken. This is done 
by keeping burette C filled to a mark, higher than the top of the 
cylinder. The cylinder is lacquered on the inside and can be used 
for lime. 




FIG. 1. 

To obtain some idea of the accuracy of the measurements made, 
the following experiments on the volume of a glass stopper are 
given : 

Number of test I ll m iv V 

Zero reading in cc 25.45 58.9 20.70 59.85 57.65 

Taken out in cc. 50.00 0.0 50.0 0.0 0.0 

Total cc 75.45 58.9 70.70 59.85 57.65 

Final reading 34.50 17.9 29.95 18.90 16.65 

Volume in cc 40.95 41.00 40.75 40.95 41.00 

The average volume was 40.93 cc. and the maximum error was 
0.18 cc. in 40.93 cc. equaled 0.44 per cent. This error, however, 
was relatively small because the stopper could be dried and 



l6 A STUDY OF THi: CHANGES IN SKINS 

always brought to a certain condition of surface moisture, not a 
varying one, as was the case with skins. The removal of liquid 
which was made necessary whenever the volume exceeded about 
50 cc. was best accomplished by means of a pipette. The liquid 
was drawn up into the burette after a measurement had been 
taken, by means of a rubber tube attached to the burette and to 
a suction pump. The procedure was as follows: Some of the 
liquid to be used was put into the cylinder A and the burette filled 
by applying suction. The stop cock was closed, the cylinder filled 
and the cover screwed down to a certain mark. The stop cock 
was then opened and the liquid allowed to run into the cylinder 
until the meniscus in the glass tube G was even with the mark. 
A reading of the burette gave the zero reading. The liquid was 
sucked back into the burette, the cover taken off, the sample 
placed in the cylinder and, if the volume was large, some of the 
liquid was pipetted off. The cylinder was then closed and a read- 
ing taken as before. This gave a final reading and from it and 
the zero reading the volume was easily calculated. The skin to 
be measured was always dried with a moist cotton cloth which 
was wrung as dry as possible. The skin was always measured 
in the same liquid in which it was at that stage of the experiment, 
that is, when in the limes, in lime water ; when in pickle, in pickle 
solution, etc. Duplicate determinations on pieces of skin whose 
volume was from 200 to 400 cc. agreed within about i cc. When 
dry skins were to be measured the cylinder was filled with water. 
The skin naturally absorbed some water, but if the experiment 
was performed rapidly, the error was not large, as was shown by 
the following experiment : 

Zero reading 56.75 

Final reading 14.25 

Volume 42.50 after i minute 

42.65 after 2 minutes 

42.85 after 3 minutes 

42.70 after 4 minutes 

42.95 after 5 minutes 

43.00 after 10 minutes 

43-1 after 15 minutes 

43.3 after 20 minutes 

The change in volume due to water absorption is very small. 



A STUDY OF TPIE CHANGES IN SKINS 17 

To test the absolute accuracy of the method this same piece of 
skin was dried and its volume remeasured. The agreement was 
within 0.5 cc. One difficulty to be guarded against in measuring 
dry skins is the tendency of air bubbles to adhere to the hairs. 
This can be avoided by shaking the whole apparatus just prior 
to taking measurements. 

Experimental Work on Voeume Changes of Calfskins. 

Nine sets of tests involving measurements of volume changes 
on twenty-one different pieces of skin are reported here. Micro- 
scopic sections from some of these sets have been referred to 
previously. The full data are given under the separate headings, 
but the sets may be outlined as follows : 

S-25 — A half-calfskin split along the backbone and trimmed, 
cut into three pieces of about equal size at right angles to the 
backbone. Carried through the tanning process. Changes in 
weight of the pieces were also noted and the density at each stage 
computed. 

S-26 — A half calfskin as above was carried through the whole 
process as one unit. Measurements of surface area and weight 
were included. 

S-27 — A piece of calfskin carried through the limes only. 

S-28 — Duplicate of 26. 

S-29 — A half calfskin was cut parallel to the backbone to 
make one piece back and the other flank. Carried through the 
limes. 

S-31 — Duplicate of 29, but carried only through soaking 
process. 

S-36 — A whole calfskin trimmed and cut into six pieces. Pro- 
tective action of lime soap tested. 

S-39 — Duplicate of 25. 

S-39B — Duplicate of 29. 

Experiment S-25. 

A dry salted calfskin was split along the backbone and one half 
was trimmed and cut into three pieces of about equal size at right 
angles to the backbone. The piece nearest the head was marked 
I, the middle piece II, and that nearest the tail III. These pieces 
were soaked in water three days, the water being changed every 
12 hours. They were then placed in limes, made by using 5 



l8 A STUDY O^ THE CHANGES IN SKINS 

grams of slaked lime to 400 cc. of water, a portion of old lime 
being added to inoculate the new lot. It was bated in a bran 
drench and pickled in salt and sulphuric acid solution made by 
taking 3 grams of concentrated sulphuric acid and 36 grams of 
salt in 850 cc. of water. The tannage was by Dennis's one-bath 
chrome method. In the following tables and curves the changes 
in volume and weight are calculated on the volume and weight of 
the skin after J2 hours soaking in water instead of on the dry 
skin. This follows the usual custom of basing all computations 
on the wet hide and allows comparison to be made with green 
hides. 

EXPERIMENT S-25.— Changes in Density. 

Condition of skin. Number I Number II Number III 

In water 72 hours 1.08 i.io 1.12 

In lime 24 hours 1.09 i.io 1.13 

In lime 48 hours 1.08 1.06 1.06 

In lime 72 hours i .08 i .09 1.05 

In lime 96 hours 1.05 1.05 1.03 

In lime 120 hours 1.06 1.07 1.04 

In lime 144 hours 1.07 1.08 i.io 

In lime 168 hours 1.07 1.08 1.09 

In lime 192 hours 1.07 1.07 1.08 

Unhaired and fleshed ... 1.07 1.05 

Bated 1.04 1.03 

Pickled 1.06 1.06 

Tanned 1.06 1.07 

Experiment S-26. 
A dry salted calfskin was trimmed and split along the back- 
bone. It was intended to carry a half -skin through the experi- 
ment as one piece but the apparatus for volume measurements 
was found to be too small so it was split into two pieces. The 
figures for the two pieces have been added together so that the 
result is reported as if it had been kept as one piece. Measure- 
ments are reported on volume, weight, area and density through- 
out the tanning process. These pieces were soaked for 24 hours 
in water, the latter being changed after 12 hours. The lime used 
was made by dissolving 5 grams of dry hydrated lime in 400 cc. 
of water. The pieces were placed in this solution for ten days. 
The lime was changed every 48 hours and a new lime of the 
same concentration was prepared. After liming until the hair 
slipped easily, the skins were placed in warm water for a few 
minutes, unhaired and fleshed. 



A STUDY OF TH^ CHANGES IN SKINS 



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A STUDY OF THE CHANGES IN SKINS 
EXPERIMENT 25.— Density. 



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A STUDY OF the; CHANGES IN SKINS 



23 



EXPERIMENT 25.— Volume. 
Per cent, increase on third soaked volume. 







EXPERIMENT 26.— Volume. 
Per cent, increase on 24-hour soaked volume. 




24 



A STUDY O^ THE CHANGE:S IN SKINS 



EXPERIMENT 26.— Weight. 
Per cent, increase on 24-hour soaked weight. 




EXPERIMENT 26.— Density. 



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A STUDY OF the: CHANGES IN SKINS 2$ 

The samples were bated three hours in an N/io sohition of 
lactic acid, in a drum. They were pickled about five hours in 
an N/50 solution of salt and sulphuric acid. They were then 
placed in a drum with a normal salt solution for one hour and 
chrome-tanned by the one-bath process. Sections were also cut 
daily during this series, as has been mentioned in the discussion 
of the microscopic study. The results are given in the accom- 
panying table and curves. 

Experiment S-27. 

In this test a piece of dry salted calfskin was used. It was 
soaked in water 24 hours. The water was changed after 12 hours. 
A lime solution containing 5 grams of slaked lime in 400 cc. of 
water was used to unhair the skin. The hide was in the limes 
seven days. Sections and volume measurements were made daily 
and the results tabulated. 

EXPERIMENT S-27 Changes in Volume, Weight and Density. 



Condition of the skin 
Dry sailed 


Volume 
in cc. 

83.3 


Increase 
in cc. 

— 154.6 


Per cent, 
increase 

—65.0 


Weight 
ing. 

92 ■ 


Increase Per cent, 
in g. increa.se 

-169 —64.7 


Density 
1. 10 


In water 24 hours- 


237-9 


0.0 


0.0 


26 r 


0.0 


0.0 


1. 10 


In lime 24 hours. . 
In lime 48 hours. . 
In lime 72 hours. . 


335-6 
356.2 
354-1 


97-7 
118.2 
116.2 


41. 1 
49.8 
48.9 


380 
374 
365 


119 

113 
104 


45-6 
43-3 
39-9 


I. 12 
1.05 
1.03 


In lime 144 hours. 
In lime 168 hours. 


342.4 
343-6 


104.5 
105.7 


44.0 
44-5 


360 
357 


99 
96 


37-9 
36.8 


1.05 
1.04 



Experiment S-28. 
In this experiment a piece of dry salted calfskin was used. The 
piece of skin was soaked in water 24 hours, the latter having 
been changed after 12 hours. The limes used were of the same 
concentration as in Experiment 26. The pieces of hide were 
limed 6 days. Volume, weight and area measurements were 
made daily. The skins were limed, unhaired and fleshed, bated 
in an N/io solution of lactic acid and followed by a bran in- 
fusion. They were pickled in an N/50 solution of sulphuric acid 
and salt and tanned by the method given in the previous experi- 
ment. The product was fair. Analysis showed 5.6 per cent, ash 
while a standard sample had 5.0 per cent. ash. The measure- 
ments taken are in the following table. The increase and per- 
centage increase in weight and volume are all computed on the 
volume and weight after 24 hours soaking in water. 



26 



A STUDY OF THE CHANGES IN SKINS 



EXPERIMENT 27. 
Per cent, increase on 24-hour soaked volume and weight. 



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EXPERIMENT 27.— Density. 




A STUDY OF THE CHANGES IN SKINS 2/ 

EXPERIMENT S.28 Changes in Volume, Weight, Area 
AND Density. 

Per In- Per 

Volume Increase cent. "Weight crease cent. Area in 
Condition of the skin in cc. in cc. increase in g. in g. increase sq. in. Density 

Dry salted 122.6 —181. 7 —59.7 135 —191 —58.6 135 i.io 

In water 24 hours • 304.3 0.0 0.0 326 0.0 0.0 161 1.07 

In lime 24 hours .. 427.2 122.9 40.3 474 148 45.4 161 i.ii 

In lime 48 hours . . 453.2 148.9 48.8 482 156 47.9 165 1.06 

In lime 72 hours • . 454.2 149.9 49-3 4^3 I57 48.1 163 1.06 

In lime 96 hours . . 455.1 150.8 49.5 484 158 48.5 164 1.06 

In lime 120 hours • 476.0 171.7 56.5 501 175 53.7 164 1.05 

In lime 144 hours . 463.0 158.7 52.1 497 171 52.5 160 1.07 

Unhaired and fleshed 220.2 — 84.1 — 27.6 231 — 95 —29.1 178 1,05 

Bated 184.5 — 119.8 — 39.3 192 — 134 — 41. i — 1.04 

Pickled 129.3 —175.0 —57.5 145 —181 —55.5 166 1. 12 

Chrome tanned 142.5 — 161. 8 — 53.1 158 —168 —51.5 151 i.ii 

Experiment S-29. 
In order to show whether the flank absorbs more water than 
the butt, a piece of each kind was used in this experiment. Num- 
ber one was a piece of calfskin butt and number two, a piece of 
flank from the same skin. These pieces were always treated in 
the same manner, in the same solutions. The hides were soaked 
48 hours in water, this being renewed every 12 hours. The limes 
contained 5 grams slaked lime per 400 cc. of water. The liming 
continued for 4 days and during this time volume measurements 
were made daily. The results follow : 

EXPERIMENT S-29.— Changes in Volume of Butt and Flank. 

Number I, butt Number II, flank 



Volume Per cent. Volume Per cent. 

Condition of the skin in cc. increase in cc. increase 

In water 48 hours 87.1 — 134.8 — 

In lime 24 hours 126.2 44.8 208.4 54-7 

In lime 72 hours 138.2 58.8 244.8 82.2 

In lime 96 hours • 141. 7 62.7 258.4 92.0 

Experiment S-33. 
The following experiment was made with pieces of dry salted 
calfskin. Two pieces were taken; number one being from the 
flank and number two from the butt. The hides were soaked 
24 hours in water, this being changed after 12 hours. The 
volume was measured before and after soaking. 



28 



A STUDY 01^ THE CHANGE:S IN SKINS 



EXPERIMENT 28.— Volume. 
Per cent, increase on 24-hour soaked volume. 




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EXPERIMENT 28.— Density. 




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A STUDY OF the: CHANGES IN SKINS 



29 



EXPERIMENT 28.— Weight. 
Per cent, increase on 24-hour soaked weight. 



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30 A STUDY OF THE CHANGES IN SKINS 

EXPERIMENT S-33.— Changes in Volume of Flank and Butt 
During Soaking. 

Number I, butt Number II, flank 



Volume Percent. Volume Percent. 

Condition of the .skin in cc. increa.se Conditioti of the skin in cc. increase 

Dry salted ... . 60.4 — Dry salted 56.2 — 

After 24 hours in water 75.4 25 After 24 hours in water 81.2 45 . 

Experiment S-39B. 
This experiment was made to confirm the results of Experi- 
ment S-29. Two pieces of dry salted calfskin were soaked for 
48 hours in water, which was changed every 12 hours. The 
pieces were limed in a solution of 5 grams of lime in 400 cc. of 
water, for 5 days. They were unhaired and fleshed, bated with 
lactic acid, pickled with sulphuric and salt, and chrome tanned 
in the same manner as stated in Experiment S-28. One piece was 
from the butt. No. i, the other. No. 2, was from the flank. Vol- 
ume measurements were taken daily and the results tabulated. 

EXPERIMENT S-39B Changes of Volume of Butt and Flank. 

Number I, butt Number II, flank 

Volume Increase Per cent. Volume Increase Per cent. 
Condition of the skin in cc. in cc. increase in cc. in cc. increase 

Dry salted 45.3 — 31.1 -40.7 45.3 —42.5 -48.5 

In water 24 hours 72.8 — 3.6 — 4.1 84.4 — 3.4 — 3.9 

In water 48 hours 76.4 0.0 0.0 87.8 0.0 0.0 

In lime 24 hours 103.8 27.4 35.8 117. 5 29.7 33.8 

In litne 48 hours 110.2 33.8 44.2 125.9 38.1 43.4 

In lime 96 hours 119.1 42.7 55.9 143.2 55.4 63.1 

In lime 120 hours 122.5 46.1 60.3 150.2 62.4 71. i 

Unhaired and fleshed 61,3 — 15. i — 19.8 81.3 — 6.5 — 7.4 

Bated 51.8 —24.6 —32.2 68.8 —19.0 —21.6 

Pickled 42.0 —34.4 — 45-0 52.5 —35-3 —40.2 

Chrome tanned 51.5 —24.9 —32.6 62.7 —25.1 —28.6 

Experiment S-39. 
This is in general a duplicate of Experiment S-25. Three 
pieces of dry salted calfskin were limed in a solution of 5 grams 
of slaked lime in 400 cc. as in previous experiments, and volume 
and weight measurements made daily. The results follow in 
table, Experiment S-39. The increase and percentage increase 
in weight and volume are computed on the weight and volume 
of the skin after 48 hours soaking in water, respectively. 



A STUDY OF the: CHANGES IN SKINS 



31 



EXPERIMENT S-39. 



Condition of the skin 

Dry salted 150.6 

In water 24 hours 
In water 48 hours. 258.3 
In lime 24 hours. . 
In lime 48 hours. • 
In lime 72 hours. . 
In lime 96 hours. . 
In litne 120 hours. 
In lime 144 hours. 
In lime 168 hours. 
Unhaired and 
fleshed 236 



-Changes in Volump:, 
OF Shoulder. 
Number I. 



Weight and Density 



V'olnme 


Increase 


Per cent. 


Weight 


Increase 


Per cent. 




in cc. 


in cc. 


increase 


in g. 


ing. 


increase 


Den.si 


150.6 


— 107.7 


—41.7 


— 


— 


— 




2530 


—5-3 


— 2.1 


— 


— 


— 




258.3 


0.0 


0.0 


287 


0.0 


0.0 


I. II 


346.0 


87.7 


34.0 


384 


97.0 


33.8 


I. II 


380.5 


122.2 


47-3 


418 


131 


45-6 


1. 10 


422.0 


163.7 


631 


455 


168 


58.5 


1.08 


440.0 


181. 7 


70.4 


475 


188 


65.5 


1.08 


416.5 


158.2 


61.3 


449 


162 


56.5 


1.08 


429.0 


170.7 


66.1 


472 


185 


64.5 


1. 10 


421.0 


162.7 


63.0 


444 


157 


54.7 


1.08 



—21.5 



256 



-31 



—10.8 —1.08 



Changes In Volume, Weight and Density of Flank. 

Number II. 

Volume 
Condition of the skin in cc. 

Dry salted 105.9 

In water 24 hours. 221. i 

In water 48 hours. 228.1 

In lime 24 hours.. 324.0 

In lime 48 hours.. 359.5 

In lime 72 hours.. 375.0 

In lime 96 hours.. 410.0 

In lime 120 hours. 432.0 

In lime 144 hours. 395.0 

In lime 168 hours. 369.5 
Unhaired and 

fleshed 226.5 

Changes In 



Increase 


Per cent. 


Weight 


Increase 


Per cent. 




in cc. 


increase 


ing. 


ing. 


increase 


Deusi 


— 122.2 


-53-5 


— 


— 


— 


— 


— 7-0 


- 3.1 


— 


— 


— 


— 


0.0 


0.0 


252 


0.0 


0.0 


I. II 


95-9 


42.0 


357 


105 


41.7 


1. 10 


1314 


57-4 


395 


143 


56.7 


1. 10 


146.9 


64.4 


412 


160 


63.5 


1. 10 


181.9 


79-7 


430 


178 


70.6 


1.05 


203.9 


89.4 


469 


217 


86.1 


1.09 


166.9 


73-1 


435 


183 


72.6 


1. 10 


141-4 


62.0 


403 


151 


59-9 


1.09 



— 1.6 — 0.7 



245 



-7.0 



2.8 



1.08 



Volume, Weight and Density of Butt. 
Number III. 





Vohime 


Increase 


Per cent. 


Weight 


Increase 


Per cent. 




Condition of the skin 


in cc. 


in cc. 


increase 


ing. 


ing. 


increase 


Densi 


Dry salted 


86.0 


-III. 7 


-56.5 


— 


— 


— 


— 


In water 24 hours. 


183.8 


-- 13.9 


— 7-0 


— 


— 


— 


— 


In water 48 hours. 


197-7 


0.0 


0.0 


219 


0.0 


0.0 


I. II 


In lime 24 hours.. 


255-0 


57-3 


29.0 


284 


65 


29.7 


I. II 


In lime 48 hours-. 


292.0 


94-3 


47.6 


322 


103 


47-0 


1. 10 


In lime 72 hours. . 


300.0 


102.3 


51.8 


334 


115 


52.5 


I. II 


In lime 96 hours. . 


318.0 


120.3 


60.9 


349 


130 


59-3 


1. 10 


In lime 120 hours. 


325-0 


127.3 


64.4 


357 


138 


63.0 


1. 10 


In lime 144 hours. 


327-5 


129.8 


65-7 


362 


143 


65-5 


I. II 


In lime 168 hours. 


296.0 


98-3 


49-7 


325 


106 


48.4 


1. 10 



Unhaired and 
fleshed 216.0 



^8.3 



9-3 



235 



16 



7-3 



1.09, 



32 



A STUDY OF the; CHANGES IN SKINS 



EXPERIMENT 39-B.— Volume. 
Per cent, increase on 48-hour soaked volume. 




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A STUDY OF the: CHANGES IN SKINS 



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Per cent, increase on 48-hour soaked weight. 



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EXPERIMENT 39.— Volume. 
Per cent, increase on 48-hour soaked volume. 




34 A STUDY OF the: CHANGE:S IN SKINS 

Attempts to Prevent Thinness of Flank. 

In looking for some remedy for the excessive swelling and sub- 
sequent looseness of the flank, the following experiments were 
made. The reasoning was that the flank was thinner than the 
rest of the skin and hence had lost more inter-fibrillar substance 
by solution. If the flank could be protected in some manner 
this would be partially prevented and the resulting leather should 
not have so thin and flabby a flank. Some substance had to be 
used which was easily applied and relatively pliable. The use of 
aluminum soap was suggested and it was tried. The hides were 
painted with a hot lo per cent, solution of aluminum sulphate 
and left a few minutes. Then the hides were painted with a hot 
lo per cent, solution of ivory soap. The pieces were then limed 
,in the usual manner. The results of various experiments follow. 

Experiment S-31. — Two pieces of calfskin which had been 
soaked 24 hours in water were painted thickly with a hot 10 per 
cent, solution of aluminum sulphate. One of these pieces was 
immediately placed in milk of lime, the other, after standing 10 
minutes, was painted thickly with a hot 10 per cent, solution of 
ivory soap. A third piece was limed 24 hours, washed thoroughly 
in water, painted with a hot 10 per cent, soap solution and finally 
returned to the limes. All three pieces gave the same result so 
far as could be detected by the ordinary methods of testing the 
quality of leather. The hair slipped just as easily as in the ordi- 
nary cases and the flank was neither fuller nor firmer. The 
results were negative. 

Experiment S-34. — Two pieces of calfskin were taken after 
24 hours soaking in water. One was soaped completely three 
times and then painted three times with an aluminum sulphate 
solution. The other was soaped and painted once on the flank 
only. These pieces were limed as usual and sent to the tannery 
to be chrome tanned and finished. All three pieces apparently 
gave the same result. No appreciable differences were noticed. 
The hair slipped just as readily as though the pieces had been 
limed in the ordinary manner. The leather appeared to have a 
better grain, but subsequent tests failed to confirm this conclusion. 

Experiment S-35. — Eight pieces, which had been soaked 24 
hours in wateV, were painted and soaped, four completely and 



A STUDY OF THE CHANGES IN SKINS 35 

four only on the flank. They were then limed and tanned. After 
tanning the tests showed negative results. It was impossible to 
tell by inspection the soaped from the unsoaped area nor did any 
of the pieces differ apparently from normally limed and tanned 
skins. 

The above experiments were all repeated using a lo per cent, 
soap solution only. The moment the hides entered the limes a 
lime soap was formed. The results of these experiments were 
almost identical with the previous ones. 

The process was studied more quantitatively in Experiment 
S-36, where in order to study the protective action of soap on 
various parts of the hide a dry salted calfskin was split down 
the backbone into two pieces, each of which was again cut at 
right angles to the backbone into three portions. The pieces on 
the left side were number i, 2 and 3 starting at the shoulder and 
those of the right side, 4, 5 and 6 respectively. The object was 
to note the various increases in volume and changes in structure 
occurring in the process. Sections were cut parallel to and at 
right angles to the backbone, after 48 hours soak, after 96 hours 
liming and just after removing from the limes. The pieces were 
cut in each case from a piece of skin taken from the backbone 
edge and the flank edge of the sample. The samples were sub- 
jected to various treatments as follows : 

No. I. — Limed 168 hours in the regular manner. 

No. 2. — Limed 144 hours, until flank unhaired easily, but butt not 

so readily. 
No. 3. — Limed 196 hours, 2 days over-limed. 
No. 4. — Soaped (10 per cent, solution) all over and limed normally 

168 hours. 
No. 5. — Soaped flank only and limed normally 168 hours. 
No. 6. — Soaped all over and over-limed 2 days, 196 hours in all. 

The sections showed that the flank was decidedly of a looser 
structure than the rest of the skin. The loose structure was noted 
in the very beginning of the process and the soap treatment 
apparently failed to remedy this defect. Even if the lime soap 
formed should hinder further action of the lime, it could not 
change the existing loose structure into a compact one. The 



36 



A STUDY OF^ THE CHANGES IN SKINS 



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A STUDY OF THE CHANGES IN SKINS 



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38 



A STUDY OF THE CHANGES IN SKINS 



EXPERIMENT 36.— Voi^ume. 
Per cent, increase on 48-hour soaked volume. 




EXPERIMENT 36.— Volume. 
Per cent, increase on 48-hour soaked volume. 




A STUDY OF THE CHANGES IN SKINS 39 

samples were all unhaired, fleshed, bated, pickled and chrome 
tanned and pronounced fair leather. The grain in all samples 
was good and showed that the soap treatment caused no apparent 
harm. The volume measurements are given in table, Experiment 
S-36, and are shown also in curves. 

Some attempts were made to fill the flank so that it would be 
as full as the rest of the skin. The hides after depilation were 
suspended in i, 2, 5 and 10 per cent, solutions of glue and a 
few cubic centimeters of methylene blue were added. The dye 
showed the extent of penetration of the solution. After the usual 
chrome tannage, the results obtained were unsatisfactory. Some 
flanks appeared to have been improved and others were as if they 
had not been treated with glue. Then i, 2, 5 and 10 per cent, 
gelatine solutions were tried. The results were practically the 
same as before. In both cases the finishing of the leather was 
attended by difficulties. Some pieces took too great a gloss and 
others remained too dull. In the next series fresh blood and glue, 
blood and gelatine were used. About 50 per cent, of blood and 
50 per cent, of a 10 per cent, solution of glue or gelatine were 
used. Although great care was taken to watch the hides care- 
fully, many were destroyed by bacteria. Even the addition of 
germicides, such as mercuric chloride and phenol failed to take 
care of the putrefactive bacteria. So long as bacterial limes are 
used this process will be attended with very great difficulties and 
can hardly be made commercial. 

Some experiments were tried on pickled stock using glue and 
gelatine to fill the flanks. The results did not justify the contin- 
uation of work along these lines. 

The greatest dfficulty in experiments of this kind is that the 
judgment of an expert is required to determine improvements. 
Moreover, improvements of a commercial value must be notice- 
able not only to an expert but also to the layman. 

ResuIvTs of Studies of Changes in Weight, Volume and 
Area of Calfskin During the Tanning Process. 

The results of these tests can best be studied from the curves 
which are computed to a common basis of percentage change 
from the condition existing when the skin entered the limes. 



40 A STUDY OF THE) CHANGES IN SKINS 

Measurements of change in superficial area were made in Experi- 
ments 26 and 28 and are given in detail in the tables. 

The dry salted skins expanded 27.1 and 19.4 per cent, re- 
spectively in area during the soaking process but both remained 
relatively constant in area throughout the subsequent operations 
of liming, bating and pickling. No. 28 showed a considerable 
increase after unhairing but this mechanical stretching disap- 
peared in the pickle. Through an oversight the area of the wet 
tanned skin was not determined in Experiment 26 and the area 
for the dried finished leather while about 5 per cent, greater than 
that of the dry salted skin, has little significance on account of 
the impossibility of standardizing the amount of stretching the 
leather received in the drying process. The leather of S-28 meas- 
ured wet showed a shrinkage in area of about 10 per cent, com- 
pared with the pickled stock and an increase in area of about 12 
per cent, compared with the dry skin. 

A comparison of the weight and volume curves of all experi- 
ments shows great general similarity. Both volume and weight 
increase in approximately the sams ratio during the soaking and 
liming process. The increase is rapid during the first 24 hours 
in water and slower after that time. On putting into lime the in- 
crease is again very rapid during the first 24 hours and becomes 
slower thereafter, reaching a maximum after about 5 days in lime. 
These limes were all bacterial but did not contain added sulphides. 

The increase in volume of different pieces varies from 40 to 
80 per cent. The experiments on changes in area quoted above 
show that very little change took place after the skin was soaked. 
These changes in volume are therefore an almost direct measure- 
ment of changes in thickness. This increase in volume and hence 
approximately of thickness runs up to a maximum of 90 per cent, 
over that of the soaked hide. The least total increase in volume 
shown by any skin is 38 per cent, over that of the soaked hide. 

Marked dififerences exist between different portions of the 
same skin limed in the same solution. In each Experiment 25, 
36 and 39 a half calfskin was trimmed and cut at right angles to 
the backbone into three pieces of approximately equal size. These 
three pieces \yere carried through the whole operation together. 



A STUDY OF THE CHANGES IN SKINS 4I 

The differences in the maximum amount of swelling of these 
three skins during the liming process is as follows : 

Shoulder Middle Rump 

Per cetit. Per cent. Per cent. 

Experiment 25 51 40 62 

Experiment 36 72 80 88 

Experiment 39 70 90 65 

No conclusions can be drawn except that different portions of 
a dry salted skin may Swell very differently in the limes. This 
may be due to differences in thickness, in structure, in amount of 
fat or to other causes and is discussed somewhat later. 

While the curves show that the changes in volume and weight 
are in general similar, the exact relationship is shown in a very 
similar manner by the curves of density. Tests 25, 26, 2y, 28 and 
39 are available for a study of this relationship. Any errors of 
measurement are magnified in this method of treatment and as 
is to be expected the curves are not altogether consistent. Cer- 
tain general features are, however, clearly recognizable. The den- 
sity decreases on soaking in water, but usually increases or 
stays constant during the first 24 hours in limes. It then de- 
creases as the liming process proceeds and reaches a maximum 
after 96 hours in the limes. It then rises to a distinct maximum 
after 144 hours in lime but usually falls again within the next 
day or two. The density falls again in the bating process 
whether a bran drench or lactic acid be used and rises sharply 
in the pickle to fall again somewhat in the wet tanned leather. 

The changes are in general those which would be expected 
when a material heavier than water absorbs water and swells. 
Ths volume increases more rapidly than the weight. The same 
phenomenon persists in the limes. The sharp change in the curve 
while still in the limes is unexpected but may be in some way 
connected with bacterial action. The immersion in the feebly 
acid bath swells the hide more rapidly than the weight increases 
and hence the density falls again. The pickle shrinks the skin 
and brings its density back to a figure nearly that of the dry skin. 

The most noticeable defect in calfskins is the flabbiness of the 
flank. Microscopic examination showed this part of the skin to 
be of loose structure and thinner than the rest. The relative 
swelling of butt and flank was tested in Experiments 29, 33 and 



42 A STUDY OF THE: CHANGES IN SKINS 

39B. In every case the flank swelled more than the butt, the 
figures for maximum increase in volume on 24 hours soaking 
over the dry volume being: 

Butt Flank 

Per cent. Per cent. 

Experiment 33 25 45 

Experiment 39B 61 86 

The maximum swelling in lime referred to the volume after soak- 
ing 48 hours was : 

Butt Flank 

Per cent. Per cent. 

Experiment 29 63 92 

Experiment 39B 60 71 

The effect of coating the flesh side of a calfskin with lime soap 
at the time of its immersion in the limes is shown in the table 
and the two sets of curves in Experiment 36. The soaped pieces 
all swelled decidedly more than the unsoaped. The maximum 
swelling expressed in j^ercentage increase on the wet volume is 
as follows: 

Not soaped Soaped 

Shoulder 38 72 

Middle 45 81 

Rump 68 88 

The volumes of the soaped pieces decrease more after unhairing 
and fleshing than do those of the unsoaped, so that the effect of 
the soap seems to be lost. Volume measurements were discon- 
tinued after this point and therefore quantitative figures on the 
finished leather are not available. However, the pieces which 
had been soaped before liming seemed slightly fuller. 

Study of Deputation in Sterile;, Limes — Review of 
Literature. 

Although the bacteria of bating and puering have been studied 
quite thoroughly, those of the limes have been more neglected. 
While certain agents have been known for some time, which 
without the aid of bacteria, were able to depilate a hide, still in 
the ordinary processes used in practice, the presence of bacteria 
was not only taken for granted, but if through any reason 
bacteria were absent active cultures were always added. This 
idea has had so firm a hold that, whenever a new tannery was 



A STUDY OF THE CHANGES IN SKINS 43 

established some old lime from another tannery was conveyed to 
the new lime pits in order to "start," that is inoculate them. 

The idea that a solution of lime could, under sterile conditions, 
cause loosening of the hair so that a hide could be unhaired easily, 
was considered impracticable. Parker^^ states, ''Formerly it was 
believed that the lime swelled the fibers of the hide, dissolving 
the hair bulb or root and loosening the epidermis, thus rendering 
the removal of the hair easy; but the liming process is now 
known to be both chemical and physical, the loosening of the hair 
being largely due to the action of enzymes and the products of 
bacteriological action. Hides cannot be unhaired by sterile limes, 
so that the process of Payne and Pullman,^* by which the hides 
were first soaked in caustic soda and afterward in calcium 
chloride, so as to form lime within the fibers, was unworkable 
unless preceded by the soaking of the hides in a foul soak to ob- 
tain the necessary bacteriological action." He also states,^^ "It 
was fully realized that bacteriological action played an important 
part in the unhairing and that the action of old limes was largely 
bacterial and that hides could not be unhaired from a sterilized 
lime." Procter^" believed that bacteria were essential in the lim- 
ing process. Stiasny^^ states that the liming process is both a 
chemical and bacteriological one. Villon in his "Traite de la 
Fabrication des cuirs" discusses the liming and sweating proc- 
esses. He states positively^^ "L'echauffe est une fermentation 
particuliere causee par un microbe determine. L'epilage a la 
chaux est cause par la meme fermentation. Que la peau ne se 
depile pas en presence de la chaux apres sterilization." He states 
that the unhairing of skins is due to the action of definite bacteria 
and that sterilized lime will not cause unhairing of a hide. He 
sterilized his samples of hide by means of dry heat. He sub- 
jected the samples to 50° C. for 24 hours and then 110° C. for 
10 minutes. Schmitz-Dumont^^ has shown that not all the 
bacteria present were killed by this treatment. 

^^ Jour. Soc. Chem. Ind. Vol. 29, p. (1912 910). 

'* English patent, No. 2,873. 

^^ JO10 . Soc. Chem. Ind. Vol. 31, p. 371 (1912). 

'^^ Pri?i. of Leather Mfg. pp. 135, 137. 

^■^ Leather Trades I^ei'. July 2, 1913. 

^^ I'illon Traite de la Fabrication des cuirs, p. 487, 

^^ Ding. Poly t. Jour. Vol. 300, p. 140. 



44 A STUDY OF the: CHANGES IN SKINS 

' Von Schroeder^^ made many experiments along the above 
lines, and as his conclusions are different, his work will be given 
more fully. His methods were as follows : Hides were obtained 
from a tannery, washed 3 days in water, then placed in a 
saturated salt solution. The salt solution was changed until the 
hide no longer absorbed salt. The hides were kept in this salt 
solution and were considered sterile. The lime used was 
sterilized in the following manner: The lime solutions were 
placed in flasks around the neck of which cotton moistened with 
salicylic acid had been wound so that the whole could be covered 
with a Petri dish. These flasks were placed in a water bath up 
to I inch from the top of the neck in water. The bath was then 
heated to boiling and kept boiling 3^ hour. This treatment was 
repeated on 3 successive days. This lime solution, was then 
called sterile. In order to observe the action of sterile water on 
hides, several flasks of water were treated precisely like the lime 
solutions. The sterile hides were placed in the sterile lime and 
sterile water flasks June 29th. On July 4th, a sample was taken 
from a water and a lime flask. No odor was perceptible in either 
case. The hair could be removed with great difficulty and in fact 
it was almost impossible to get it off. One cubic centimeter of 
the water and one of the lime solution were now transplanted into 
10 cc. of gelatine. All these sub-cultures gave a positive result, 
that is a growth of bacteria or molds, whereas if the solution had 
been really sterih there should have been no growths. On July 
nth a flask of each kind was again opened. The hair slipped 
easily. Again all sub-cultures made gave positive results. On 
August 3rd the remaining flasks were opened and all sub-cultures 
again gave positive results. Moreover, the solutions all had a 
putrid odor. 

Van Schroeder then took part of the water in the flasks, added 
it to some sterile limes and the sub-cultures made showed few 
colonies. His conclusion was that the lime killed the bacteria 
contained in the water. His final conclusion based on this last 
experiment was that in the limes, unhairing takes place without 
bacterial action in a short time, but that in pure (reinem) water 
only after bacteria have developed and produced ammonia 
enough to make the solution alkaline. His second series was as 
20 Ding. Polyt.Jour. Vol. 30T, pp. 65, 90, 



A STUDY OF THE CHANGES IN SKINS 45 

follows : The hides from the saturated salt solution were placed 
in 99 per cent, alcohol which was renewed every day for 4 days. 
These hides were considered sterile. The flasks containing water 
and lime water solutions were sterilized as before. All except 
one of the sub-cultures taken after 4 days gave positive results. 
In this case some hairs were transplanted to gelatine by means 
of a forceps sterilized in a flame. There is a possibility that the 
forceps was too hot and killed the bacteria, or that the melted 
gelatine was too warm. After 6 days two more flasks were 
opened and sub-cultures made. All but two gave positive re- 
sults. These two sub-cultures were made by transplanting o.i cc. 
and o.oi cc. of the lime solution in 10 cc. of gelatine. The final 
conclusion drawn from these experiments was that "Die Vor- 
bereitung der Haut zum Enthaaren durch den Aescher process 
von Bakterien iiberhaupt unabhangig und nur eine Wirkung der 
alkalischen Reaction des Kalkes ist." Von Schroeder then as- 
sumes that Villon's idea that bacilkis pilline must be present in 
limes in order that the hair be loosened, is no longer true. Un- 
fortunately Von Schroeder died before the work was completed 
and the paper was published by others. The results do not bear 
out the assumption that the hides and solution used were really 
sterile. On the contrary all but two sub-cultures from the sup- 
posedly sterile solutions gave positive results. The sub-cultures 
which were negative under aerobic condtions were not duplicated 
under anaerobic conditions. There is no valid reason why an- 
aerobic bacteria could not have been present. He also neglected 
to guard against the inhibiting action of the lime. He showed at 
great length that the lime solution killed, or rather to be accurate 
inhibited the growth of bacteria obtained from the infected water 
used in the first experiment. Afterward he did not take this fact 
into consideration, but transplanted his solution from the lime 
flasks into the same amount of gelatine — 10 cc. as in the experi- 
ment using water only. 

Grifiith^^ made several experiments on a sterile liming process 
using carbon bisulphide and phenol as disinfectants. He does not 
give any data nor information about the actual methods used or 
precautions taken to prevent infection of the solutions but merely 
speaks of "pieces of hide previously sterilized with carbon bisul- 
21 Journal Amer. Leather Chem. Asso.,Vol 5, p. 115 (1910)- 



46 A STUDY OF THK CHANGES IN SKINS 

pbide and with phenol and the Hming carried out in sealed jars. 
The carbon bisulphide hide unhaired in 24 days and the phenol 
hide unhaired in 18 days and an experienced bacteriologist was 
unable to discover the presence of bacteria. Von Schroeder ex- 
perimented with fresh salted hides under sterile conditions and 
he was unable to discover that the absence of bacteria influenced 
the activity of the lime as a depilatory." The above statements 
would have been more convincing if the methods of bacterio- 
logical control had been given more fully. Griffith concedes that 
Von Schroeder's work was correct and he admits that the latter 
worked under sterile conditions. As was pointed out before this 
was not the case. Von Schroeder never had sterile conditions 
prevailing in any of his experiments as his sub-cultures always 
showed bacteria or molds. Griffith relied entirely on carbon 
bisulphide as a sterilizing agent. Carbon bisulphide may be an 
antiseptic agent but it is not a disinfectant for it does not kill all 
organisms, as was shown by Procter.^^ 

The experiment with carbon bisulphide gave approximately 
the same results as that with phenol. This may have been due to 
the fact that under the conditions existing during the experiment 
the carbon bisulphide was present in sufficient quantity to pre- 
vent a noticeable increase in the number of bacteria present. The 
above experiments cannot be accepted as accurate in the scientific 
sense. 

Experimental, Work on Sterilization oe Hides. 

The following experiments were planned to settle definitely 
whether bacteria were necessary in the depilation process. The 
sterilization of hides ofi'ered the first difficulty. After reading 
of various methods^"^ using sulphur dioxide, phenol, etc., the 
Seymour-Jones method was finally adopted as offering the best 
chances of success. The method consists of immersion of the 
hide for 24 hours in a 0.02 per cent, solution of mercuric chloride 
and a 0.5 per cent, solution of formic acid. 

In order to test Seymour-Jones method of sterilization for its 
effectiveness as a sterilizing agent the following experiments were 
made. Samples of hide about 1x2 centimeters were soaked in 
■" Procter, Principles of Leather Manufacture, p. 135. 
2^ Journal Amer. Leather Chem. Asso., Vol 5, pp. 508-10. 



Anaerobic 






conditions. 






in a 






l>!ovy jar, over 






hydrogen. L,it- 


Check for 


Check 


mu.s gluco.se 
geliitine 


Anaerobes 


Aerobes 


B. tetanus 


B. lactici 


— 


+ 


+ + + + 


— 


+ 


+ + + + 


— 


+ 


-[- + + + 



A STUDY OF THE CHANGES IN SKINS 47 

the solution 24 hours. They were then removed with sterile for- 
ceps and washed three times by immersion, using a liter of 
sterile water each time. Then they were planted by means of 
sterile forceps into 150 cc. of sterile medium, beef tea, gelatine, 
agar, pea-bean medium, and litmus glucose gelatine being used. 
The results are shown in the table. 



Seymour-Jones Test. 



No. Beef tea Gelatine Pea-bean Agar 



Although these solutions all showed negative results it is neces- 
sary, before admitting the test to be conclusive, to show that the 
amount of mercuric chloride transferred could not have been 
sufficient to have inhibited the growth of bacteria in the culture 
media. Mercuric chloride acts as an antiseptic agent even in 
dilutions of i to 100,000. The samples after washing thoroughly 
in 3 liters of sterile water had very little mercuric chloride ad- 
hering. Moreover, the volume of medium used was large, 150 cc. 
or more in all cases. This again increases the dilution of the 
mercuric chloride and hence eliminates its antiseptic action. 

The dilution at which formic acid still exerts its antiseptic 
action is not known definitely. The fact was taken into consid- 
eration, however, that the antiseptic action of formic acid is 
usually less than that of mercuric chloride. If one assumes the 
piece of hide transferred, to be all formic acid, and then takes 
into consideration the dilution resulting from the washing in 
sterile water, one will see that the dilution is more than i to 
200,000 and that there is no chance of any antiseptic action inter- 
fering with the results. In order to check whether the medium 
was suitable for growing bacteria, bacillus tetanus and bacillus 
acidi lactici were planted under anaerobic and aerobic conditions 
respectively. The results were positive in all cases. 

Since the checks were always positive and the sub-cultures 



48 A STUDY OF THE CHANGES IN SKINS 

from the sterilized hides negative, it was therefore considered 
proven that the Seymour-Jones method of steriHzation is ef- 
fective under the given conditions of experiment. 

Tkst For Bacteria in the: Limes. 

Since there might be some question as to the presence of 
bacteria in the hmes, sub-cultures were made on agar, beef tea, 
pea-bean media and gelatine. All sub-cultures gave positive re- 
sults. 

Wood-'* has shown that bacteria of various kinds are present 
in the limes. Abt^^ has also proven that bacteria are present in 
the liming process. 

The medium used in transplanting sub-cultures in all the fol- 
lowing experiments was slightly more alkaline than that usually 
employed for this purpose. 

Expkrimentai, Work — Laboratory Tests on Depilation. 

The procedure now used was as follows: A 250 cc. Soxhlet 
flask, provided with a tight cotton plug was sterilized for i minute 
at 200° C. in a dry heat sterilizer. It was cooled and 175 cc. of 
water and 50 grams of slaked lime were added. The flask was 
then autoclaved at 110° C. for 20 minutes and allowed to cool. 
A piece of hide which had been previously sterilized in a solu- 
tion (Seymour-Jones) of 1-5,000 mercuric chloride and 0.5 per 
cent, formic acid, for 24 hours, was added to this solution by 
means of sterile forceps. This flask was then examined every 
2 or 3 days, great care being taken to prevent infection of its con- 
tents. After II days the hair could be removed with difficulty, 
but after 13 days the hide could be easily unhaired. 

In order to prove conclusively that bacteria were absent, sub- 
cultures of the- lime solution and of hair were made on various 
media under aerobic and anaerobic conditions. That the med- 
ium used was suitable for the growth of bacteria was proven by 
planting test organisms. For this purpose bacillus acidi lacHci 
and bacillus tetanus were used under aerobic and anaerobic con- 
ditions, respectively. The results obtained are shown in the fol- 
lowing table : 

^V- ^oc. Chein. Itid., Vol. 29, p. 666. (1910). 

2^ Bull. SyAdicat. Gen. Cuirs et Peau.v, p. 416, Nov. 10, 1908. 



A STUDY OF THE CHANGES IN SKINS 49 

Check Test on Sterility of Conditions. 

Under anaerobic conditions 

in a Novy j.ir previously 

exhausted and hydrogen 

passed in. 

Beef tea Gelatine Pea-bean lyitmus glucose gelatine 

I loop of lime solution . — — — — 

Hair — — — — 

Checks + + + 4- 

These results are very satisfactory and show, since all the sub- 
cultures were negative and the checks positive, that no bacteria 
capable of growing were present in the limes used. 

After it had been shown that the Seymour-Jones method of 
sterilization with mercuric chloride and formic acid was reliable 
and preliminary tests had shown that it was possible to unhair 
a skin with sterile limes, the following series of tests was under- 
taken to study the process more quantitatively. Four different 
solutions were used to determine how lime alone, and lime with 
sulphur compounds acted. One flask contained lime only, a sec- 
ond lime and red arsenic sulphide, a third, lime, red arsenic sul- 
phide and hair, and the fourth lime and hair. The solutions con- 
taining hair were boiled vigorously for 45 minutes, before use, 
with the idea that some hydrolysis of the hair would take place 
with formation of soluble sulphur compounds and amino acids 
and that thus the action of an old lime might be simulated. The 
details of the tests are as follows : 

Four pieces of dried calfskin 2x3 inches in area were soaked 
24 hours in a solution of 0.02 per cent, mercuric chloride and 
0.5 per cent, formic acid. Four 250 cc. Soxhlet flasks were 
plugged with cotton and sterilized for i minute at 200° C. in a 
dry heat sterilizer. To one of these flasks 50 grams of lime and 
175-200 cc. of water were added. To another sterile flask 50 
grams of lime, 175-200 cc. of water and 1.5 grams of red arsenic 
sulphide were added. Then the flasks which were to contain 
boiled hair were prepared as follows : 200 cc. of water, 50 grams 
of lime and 10-12 grams of hair clipped from a calfskin, were 
boiled vigorously for 45 minutes. This solution was placed in 
a sterile flask. Then 200 cc. of water, 50 grams of lime, 1.5 grams 
of red arsenic sulphide and 10-12 grams of hair were boiled 45 
minutes and put into the fourth sterile flask. Then the four 
flasks were autoclaved for 20 minutes at 110° C. A piece of 



50 



A STUDY OF THE CHANGES IN SKINS 



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A STUDY OF THE CHANGES IN SKINS 5 1 

Sterile hide was now planted in each of the flasks after cooling, 
by means of sterile forceps. 

The following table gives some of the observations made on 
these samples. Every time the hides were examined great care 
was taken to handle them with sterile instruments and in such a 
manner that they remained sterile. The flasks were all kept at 
the room temperature. They were not examined every day, for 
the danger of contamination would have increased at a greater 
rate than the notable differences in the skin. The remarks con- 
cerning the condition of the skin are rather indefinite to be sure, 
but the changes were very gradual and consisted in the main in 
such as are hard to describe accurately. 

In order that there might be no question of the sterility of the 
various flasks, sub-cultures were made on various media after 
the test had been running 2 months. Gelatine, beef tea and 
pea-bean media were used for aerobic and litmus glucose gelatine 
for anaerobic experiments. B. acidi lactici and B. tetanus were 
used as checks respectively. The results follow in the table. 
EXPERIMENT 38.— Check on Sterii-ity of Solutions. 

Number of flask I II III IV 

Gelatine plates — — — — Planted 2-12-14 

Gelatine tubes — +* — — Examined daily from 

Pea-bean tubes — — — — 2-12 to 2-24 

Beef tea tubes — — — — 

Checks + + + 4- 

Anaerobic conditions in 

Novy jar over hydrogen . • — — — — 

Litmus glucose gelatine Planted 2-12-14 

Checks -h + -|- + Examined 2-26-14 

* One positive result out of eight gelatine tubes. 

It will be noted that all the results are negative with the ex- 
ception of one of the eight gelatine tubes planted from Flask II. 
To study this organism further it was transplanted and plated. 
It proved to be a streptococcus, white, liquefying gelatine and 
was probably Matschek's white streptococcus. Then six more 
gelatine sub-cultures were made from the original flask. All 
were negative. Therefore, it is reasonable to presume that this 
one tube became infected through air and technique. The 
anaerobes were transplanted to litmus glucose gelatine and 
placed in a Novy jar. This was exhausted to 28.8 millimeters 
vacuum, then hydrogen was passed in. This process was repeated 
three times then the jar was closed and left for 14 days. No 



52 A STUDY OF THE CHANGES IN SKINS 

growths were noticeable. Tetanus bacillus was used as a check 
and gave a good growth in litmus glucose gelatine to which one 
loopful of sterile lime water had been added. In the case of 
aerobes, the check used on gelatine with one loopful of sterile 
lime was bacillus acidi lactici. In all cases the effect of the lime 
and water which was unavoidably conveyed by the platinum loop 
during inoculation, and which might have had an antiseptic or 
germicidal action, was provided for by using a large amount of 
medium at least 15 cc. in each case and to be more certain, for 
each set one flask containing 100-150 cc. of medium was used. 

This Experiment 38 was continued 5 months as shown by the 
table and at the end of the period, the flasks were again tested. 
All tubes and flasks showed negative results, that is no growths. 
The checks were all positive showing that conditions were fav- 
orable for the growth of bacteria. Details are given in the fol- 
lowing table: 

EXPERIMENT 38,— Finai^ Check on Sterility of Soi^utions. 

Number of flask I II III IV 

Planted 3-8-14 examined 

Gelatine plates — — — — daily from 

Gelatine tubes — — — — 3-9 to 3-23 

Pea-bean — — — — 

Beef tea — — — — 

Checks + + + + 

Anaerobic conditions Lit- Planted 3-8-14 

mus glucose gelatine — — — — Examined after 14 days 

Check + -h -H + 

Experiment 40. 
This experiment was made both to check results of the previous 
one and to see whether the presence of hair had any marked ef- 
fect on the changes taking place during the sterile liming. The 
samples of hide were sterilized 24 hours in Seymour- Jones solu- 
tion then transferred with sterile forceps to sterile flasks con- 
taining lime, and lime and arsenic sulphide. The samples were in 
one case hide which had had the hair closely clipped off before 
sterilization and in the other case normal hides with hair on. At 
the same time 20 grams of hair were sterilized 3 days and then 
placed in 600 cc. of water containing 50 grams of lime with the 
idea in mind of noting changes on pure hair under said conditions. 
The results follow in the table. Sub-cultures were made from 
all flasks on various media precisely as in the previous tests. The 
results were all negative and are shown in the following tables : 



A STUDY OF THE CHANGES IN SKINS 



53 



> 
a 

O 




1^ « 


Hair sterilized 3 days. 
No change. 

No odor. No change. 
Same. 

Slight odor of hydro- 
gen sulphide. 

Same. 

About thesame. Slight 
odor of ammonia and 
hydrogen sulphide. 


o 

^ >. 

2; 







Xo change, no odor. 

Hair tight, can be 
pulled; slight odor. 

Hair still tight, not 
much if any odor. 

Hair slips fairly easy, 
Corium hard like 
Number III. Flesh 
side somewhat swol- 
len. Very little odor 
if any. 

Hair slips very easily. 
Upper lay er attacked , 
it can be scraped off. 
No odor. 

Same. Same, corium 
good. 


O 
D 

Q 


1 

> 

5 


la 


mour-Jones solution. 
No change, no odor. 

No change, no odor. 

May be slight odor, 
hard to tell. Hair can 
be scraped easily. 
Corium good and 
harder than Num- 
bers I and II. 

Upper layer not soft 
like I and II. No 
odor. 

Same. Corium firm, 
same. No odor. Up- 
per layer still good. 
Slightlyattacked 
corium good and 
fi rm . 


Q 

11 

\ 


§ 

'S 


3 

CS 

u 

a 


hours sterilization in Sey- 
Hair slips very little when 

pulled strongly. 
Same. 

Hair slips more easily. 
Slight odor of hydrogen 
sulphide. 

Hair slips very easily; 
much of it dissolved. 
Epidermis attacked; 
slight hydrogen sul- 
phide odor. 

Hair nearly all gone, up- 
per layer mushy. Co- 
rium good, odor of 
hydrogen sulphide. 

Not much odor of hydro- 
gen sulphide. Upper 
layer more attacked 
than Number I. Patches 
of it gone. 

About same. No odor, 
same. Upper layer al- 
most all gone. No odor. 
Corium good. Not so 
firm. 


w 1 
;2 


> 


d 


Into all solutions after 24 
No change. 

ii ii 
i( li 

Hair slips some, that is, 
comes off on scraping. 

Hair can be scraped 
easily. Very slight odor 
epidermis attacked. 

Not much odor, may be 
slight hydrogen sul- 
phide. Upper layer badly 
aitacked. Hair all gone. 
Corium still hard and 
firm. 

Upper layer badly at- 
tacked. Corium firm 
and hard. Very little 
odor. 

About same. No odor, 
same. Upper layer very 
mushy. No odor corium 
firm. Flesh side swol- 
len. 






^ 1 





54 



A STUDY OF THE CHANGES IN SKINS 



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A STUDY OF THE CHANGES IN SKINS 55 

EXPERIMENT 40.— Check on Steruty of Solutions 
After Ten Weeks. 

Number of flask I n m iv 

Gelatine plates — — — _ Planted 2-12 examined 

Gelatine tubes — — — — Daily from 2-12 to 2-24 

Beef tea tubes — — — — 

Pea-bean tubes — — — — 

Checks 4. -f- -f- -|- 

Anaerobic conditions. Lit- 
mus glucose gelatine in Planted 2-12 examined 

Novy jar over hydrogen — — — — 2-26 

Checks -f -f -(- -(- 

EXPERIMENT 40.— Finai, Check on Sterility of Solutions. 

Number of flask I II m iv 

Gelatine plates — — — — Planted 3-9 examined 

Gelatine tubes _ _ _ — Daily after 3-10 to 3-20 

Beef tea tubes — — — — 

Pea-bean tubes — — — — 

Checks + -j- -J- -|- 

Anaerobic conditions on lit- 
mus glucose in a Novy Planted 3-9 

jar over hydrogen — — — — Examined 3-23 

Checks -^ -^ _(_ -f 

Experiments 41. 

As a final check on the previous results the following tests 
were made: Two flasks were plugged with cotton, steriHzed by- 
dry heat for i minute at 200° C. To each flask 100 cc. of water 
and 10 grams of lime were added. They were then autoclaved 20 
minutes at 110° C. Two pieces of calfskin 1x2 inches were 
sterilized 48 hours in a Seymour-Jones solution. The sterile 
hides were placed in the flask October 30, 1913. The flasks were 
left undisturbed at room temperature until March 9, 1914, when 
they were opened and sub-cultures made as in previous experi- 
ments. All sub-cultures were negative but the checks were posi- 
tive. The flask, therefore, contained a sterile solution. 

The skin had changed considerably in its 4 months treatment 
in sterile lime. The hair was all very loose; the upper layer and 
the flesh side of the skin had become mushy and swollen. The 
corium was fairly firm but glassy in appearance. No odor was 
noticeable. The preceding experiments had all been made on 
calfskin. In order to check the results on heavier hides a sample 
of sterilized cowhide was placed in a sterile lime solution Decem- 



56 A STUDY OF THE CHANGES IN SKINS 

-ber 12, 1913. This contained 5 grams of lime and 0.5 gram of 
sodium sulphide in 100 cc. of water. The hide was examined 
March 9, 1914. The flask had been left undisturbed during this 
time. Sub-cultures were made as before, and all results were 
negative. This showed that the solution was sterile. 

This hide had also changed materially by its 3 months' treat- 
ment in sterile lime. All the hair was dissolved. The upper layer 
had been dissolved and the flesh side' had not only become mushy 
as in the previous experiment, but in fact it had disappeared, 
leaving only a firm tough layer of corium, which had apparently 
suffered very little change. 

Depilation IN Sterile Solution and Subsequent 
Tannage. 

After these preliminary tests of liming under sterile conditions, 
somewhat larger pieces of hide were used and carried through 
the entire tanning process. The final products were then com- 
pared with commercial products obtained by liming in the usual 
manner. 

The first experiments were on pieces of cowhide which were 
tanned subsequently, through the courtesy of Mr. V. A. Wallin, 
in the Wallin tanneries at Grand Rapids. 

Experiment 42. Experiments on Cowhides. 

Two pieces of cowhide about i x 10 feet were sterilized 3 
days in Seymour-Jones's solution. The bottles in which the 
previous solutions had been sterilized had been made of cheap 
cast glass but had caused much trouble by breaking during ster- 
ilization, in spite of the utmost precautions taken while heating 
and cooling them. This difficulty was overcome by using narrow 
and deep galvanized iron cans 5 centimeters by 42 centimeters by 
46 centimeters. Small shelves were arranged so the hides could 
be suspended over glass rods. The solutions to be used were ster- 
ihzed in these cans by boiling over a direct flame for 4 to 8 hours. 
The cover, not fitting tightly, allowed a cloth moistened with 0.02 
per cent, mercuric chloride solution to be placed over the can in 
such a manner that it could be kept sterile. 

Hide No. i, was limed in a solution containing 5 grams of 
lime and o.^ gram of sodium sulphide crystals, in 400 cc. of 



A STUDY OF THE CHANGES IN SKINS 57 

water, for 3 days. It was removed while slightly underlimed and 
placed in a can containing a sterile saturated lime solution and 
shipped to the Wallin Tannery, Grand Rapids, Michigan, to be 
put through their regular tanning process. 

Hide No. 2, was limed in the same kind of a solution as No. i 
but for 6 days. It was removed and shipped in a sterile saturated 
lime solution. Sub-cultures made as in previous experiments 
gave negative results and showed that these hides had been un- 
haired in sterile solution. 

The finished sample of leather from hide No. i was returned 
from the tannery with the comment : 

**The job seems to be satisfactory. The stock is a little bit 
snappy on the grain but it is not certain that this has any rela- 
tion to the liming." 

The finished sample of leather from hide No. 2 has not yet 
been returned from the tannery. 

Experiment S-43. 

Two pieces of cowhide were received wet and salted. They 
were washed thoroughly in water and sterilized in Seymour-Jones 
solution for 48 hours. The limes used were made up by dissolv- 
ing 5 grams of lime and 0.5 gram of sodium sulphide in 400 cc. 
of water. They were sterilized by boiling 4 to 8 hours over a 
free flame. The hides were now treated as follows : One piece 
was limed 4 days, then placed in a sterile saturated lime solution 
and shipped to the tannery. The other piece was purposely over- 
limed and after 7 days in the lime was sent to the tannery in the 
same way as was the other piece. Sub-cultures from the limes 
used, were made on various media in the same manner as in 
previous experiments. All sub-cultures were negative and 
showed that the solutions had been sterile. 

The loss of hide substance in the liming process is often con- 
siderable and an examination was made of some of these lime 
solutions to determine the amount of hide substance dissolved. 
For comparison an old lime from the Wallin tannery was also 
tested. The hide substance in solution was calculated from the 
content of ammonia shown by the Kjeldahl method. The results 
are shown in the following table : 



58 



A STUDY OF THE CHANGES IN SKINS 



Hide Substance Dissoi^ved in Limes. 

Ammonia Hide snbstance 
vSource of lime g. per 1. g. per 1. Remarks 

Experiment 42 0.1366 0.623 Hide 3 days in 

Hide #r. 0.1326 sterile lime. 

Experiment 42 0.3145 i .457 Hide 6 days in 

Hide ^2. 0.3155 sterile lime. 

Experiment 43 0.41 14 1909 Hide 4 days in 

Hide #1. 0.4138 sterile lime. 

Experiment 43 0.9479 4-376 Hide 7 days in 

Hide #2. 0.9452 sterile lime. 

Old lime from Wallin tan 1-439 6.694 

1.454 
The amount of hide substance dissolved by these sterile limes 
is less than that shown in the old lime from the tannery but not 
enough is known of the changes of limes with continued use to 
warrant a positive conclusion. 

Experiments on Calfskins. 

Calfskins received in the dry salted state were unhaired in 
sterile limes and through the courtesy of Mr. Carl E. Schmidt, 
tanned by the chrome process in his Detroit tannery. 

Considerable difficulty had been experienced in handling the 
can used to contain the sterile limes in the previous experiments, 
and spots appeared on the hides where they touched the metal. 
The calfskins were limp enough so that glass vessels could be 
used. 

Experiment S-41A. 

A bottle of about 6 liters capacity was plugged with cotton and 
sterilized at 200° C. for i minute in a dry heat sterilized. One- 
half of a small calfskin, weighing 250 grams was sterilized 24 
hours in a Seymour-Jones solution. A lime solution containing 
5 grams of lime and 0.15 gram of red arsenic sulphide in 400 cc. 
of water was put into the sterile bottle and this was autoclaved 
at 110° C. for 20 minutes. The sterile skin was now placed in 
the sterile lime and left for 9 days. The hair slipped very easily. 
This skin was sent to the Carl E. Schmidt Tannery at Detroit, 
Michigan, where it was chrome tanned and finished. The product 
was of little value. The grain could be peeled off easily. The 
leather had very little strength and felt very thin. The liming 
had been allQwed to proceed too long and the skin had become 
seriously damaged. The grain was also drawn and harsh. 



A STUDY OF the; CHANGES IN SKINS 59 

In subsequent tests on calfskin a large Jena flask of about 15 
liters capacity was plugged with sterile cotton. The flask was too 
large to permit sterilization in a dry heat sterilizer hence it was 
only washed with distilled water. The cotton plug, after it was 
made to fit the flask was sterilized for 5 minutes at 200° C. A 
lime solution was made containing 5 grams of lime and 0.15 gram 
of red arsenic sulphide per 400 cc. of water, and put into the 
flask. This was then autoclaved 4 to 5 hours at 110° to 120° C. 

Experiment 44. 
One-half of a small calfskin was sterilized 48 hours in Sey- 
mour-Jones's solution. It was then placed in the sterile lime 
solution in the sterile flask and allowed to remain 5 days. The 
hair was partially destroyed and slipped easily, except in certain 
spots. These spots were very difficult to unhair for some reason. 
The grain of this leather cracked and scuffed easily and was not 
satisfactory. 

Experiment 45. 

The flask used in Experiment 44 containing the same lime and 
arsenic sulphide solution, was autoclaved 4 to 5 hours at 110° to 
120° C, to insure sterility of the contents. One-half of a dry 
salted calfskin which had been sterilized for 24 hours in a Sey- 
mour-Jones solution, was added to the cooled flask with sterile 
forceps. This skin was limed 6 days. Sub-cultures made pre- 
cisely as in previous experiments showed negative results and that 
the limes had been sterile. The skin unhaired easily except in one 
place an area of about 6 square inches. The white hair on this 
spot adhered with remarkable tenacity while the black hair on 
the rest of the skin slipped easily. No explanation of this peculiar 
occurrence could be suggested at the tannery. The hide felt 
"full" and the final product was of fair quality. The leather had 
average tensile strength and a good grain although it did not 
feel as full as the standard product of the tannery. Stretching 
did not crack the grain of the final product except on the extreme 
flank. 

Experiment 46. 

To the same lime solution in the flask of Experiment 45 9 
grams of red arsenic sulphide, 300 grams of slaked lime and 



6o A STUDY OF the: CHANGES IN SKINS 

enough water were added to bring the contents up to the original 
vokime. This flask was again autoclaved 4 to 5 hours at 110° to 
120° C. to insure steriHty of the contents. The piece of calfskin 
to be used was sterilized as before in a Seymour-Jones solution 
for 24 hours. The hair slipped easily after 6 days. Sub-cultures 
made from this lime solution, on various media as in previous 
experiments, showed negative results and proved the solution to 
have been sterile. The final leather felt quite "full" in the judg- 
ment of the tannery superintendent. It had a good grain and a 
tensile strength greater than that of the average skin limed in the 
ordinary manner. It had a very slight harshness which could 
probably be overcome by modification of the finishing process. 
The leather felt very full both in the flank and at the backbone. 
The flank appeared to be better than in the ordinary product. 

Conclusions. 

The foregoing paper studies from three different viewpoints 
the changes taking place in hides during their conversion into 
leather and particularly during the liming process. A study is 
made of structural changes throughout the vegetable and mineral 
tanning processes as shown by the microscope; of gross changes 
in volume, weight and density of the skin; and of the practi- 
cability of carrying out the depilation process in sterile solutions. 

Detailed methods have been worked out for the satisfactory 
preparation of microscopic sections both by the colloidin and 
freezing methods. A study of numerous sections of skin shows 
that the structural changes occurring during depilation and tan- 
nage are so gradual that only the broad outline can be followed. 
The inter-fibrillar substance in the bundles of connective tissue 
dissolves in the liming process and the fiber bundles split up into 
their component fibrils. The flank is composed of larger, fewer 
and more irregular fiber bundles with larger interstitial spaces 
than the better portions of the skin. This gives a partial explan- 
ation of the poorer quality of flank leather. 

When dry calfskins are put into water they increase in super- 
ficial area, thickness and weight but decrease in density. The 
area remains almost constant during the liming process in bacter- 
ial limes, but the volume and hence the thickness of the skin in- 
creases quite consistently and at a decreasing rate during the 



I 



A STUDY OF THE CHANGES IN SKINS 6 1 

liming process. The weight increases at approximately the same 
rate but a study of the relationship of weight and volume as 
shown by the density curves, indicates that the volume increases 
faster than the weight during the first 4 or 5 days in limes con- 
taining bacteria so that at the end of this period the hide shows 
the minimum density which it ever attains in the limes. Within 
2 days after this point is reached the volume decreases more 
rapidly than the weight and the density rises decidedly. The sig- 
nificance of these points of inflection of the curves is not evident. 
' Both volume and weight decrease in the feebly acid bate used 
but the decrease in weight is greater than that of the volume so 
that the density falls. In the pickle, conditions are the reverse 
of those in the bate and the density rises sharply. No great 
changes in weight volume or density occur during the one bath 
tannage used. 

Different pieces of the same skin while the same in general, 
show decided quantitative variations from each other. The 
shoulder, back and rump show distinct differences which are not 
constant in different skins. The flank, however, swells quite con- 
sistently more than the rest of the skin, both in water and in the 
limes. These differences may be due to the varying thickness of 
the skin or to surface conditions such as fat. If the flesh side is 
painted with a soap solution before immersion in the limes so 
that an insoluble lime soap is precipitated upon it, the swelling 
is greatly increased. 

It has been shown that it is possible to depilate a skin or hide 
under strictly sterile conditions with lime alone or with the addi- 
tion of sulphides. The same sterile lime solution can be used to 
depilate successive pieces of hide. Calfskin kept for 6 months 
in sterile milk of lime shows a firm though rather glassy corium. 
A skin kept a similar length of time in sterile milk of Hme con- 
taining arsenic or sodium sulphide, is completely dissolved. The 
hair from the skins in the latter solutions is also dissolved com- 
pletely, while that of the skin in lime alone, appears almost un- 
changed. 

Pieces of cowhide and calfskin unhaired under sterile condi- 
tions have been tanned and finished in commercial tanneries using 
vegetable and mineral tanning agents, with fair results. It seems 
entirely probably that with a little more experience in handhng 



62 A STUDY OF THE CHANGES IN SKINS 

Sterile limes a good product, equal in all respects to that produced 
by the present methods of liming could be obtained. 

BIBLIOGRAPHY. 

1. Jettmar, Handbuch der Chromgerbung (1900). 

2. Der Gerber. 

3. Procter, The Principles of Leather Manufacture. 

4. Procter, The Leather Industries Laboratory Book. 

5. Collegium. 

6. Bulletin de la Societe d'encouragement pour I'industrie. Nationale. 

7. Dinglers Poly technische Journal. 

8. Hyde, Diseases of the Skin (1909). 

9. JouRNAi, of the American Leather Chemists Association. 

10. Warthin, Practical Pathology. 

11. Journal of the Society of Chemical Industry. 

12. English Patent Number 2873. 

13. Villon, Traite de la Fabrication des cuirs. 

14. Leather Trades' Review. 

15. Bull. Syndicat. Gen. Cuirs et Peaux, p. 416, Nov. 10, 1908. 



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